Membrane Structure and Function

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Most of the lipids, and some proteins, drift laterally

Rarely does a molecule flip-flop transversely across the membrane

Slide 11

Fig. 7-5

Lateral movement

(~107 times per second)

Flip-flop

(~ once per month)

(a) Movement of phospholipids

(b) Membrane fluidity

Fluid

Viscous

Unsaturated hydrocarbon

tails with kinks

Saturated hydro-

carbon tails

(c) Cholesterol within the animal cell membrane

Cholesterol

Slide 12

Fig. 7-5a

(a) Movement of phospholipids

Lateral movement

(107 times per second)

Flip-flop

( once per month)

Slide 13

Fig. 7-6

RESULTS

Membrane proteins

Mouse cell

Human cell

Hybrid cell

Mixed proteins

after 1 hour

Slide 14

As temperatures cool, membranes switch from a fluid state to a solid state

The temperature at which a membrane solidifies depends on the types of lipids

Membranes rich in unsaturated fatty acids are more fluid that those rich in saturated fatty acids

Membranes must be fluid to work properly; they are usually about as fluid as salad oil

Slide 15

Fig. 7-5b

(b) Membrane fluidity

Fluid

Unsaturated hydrocarbon

tails with kinks

Viscous

Saturated hydro-

carbon tails

Slide 16

The steroid cholesterol has different effects on membrane fluidity at different temperatures

At warm temperatures (such as 37°C), cholesterol restrains movement of phospholipids

At cool temperatures, it maintains fluidity by preventing tight packing

Slide 17

Fig. 7-5c

Cholesterol

(c) Cholesterol within the animal cell membrane

Slide 18

Membrane Proteins and Their Functions

A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer

Proteins determine most of the membrane’s specific functions

Slide 19

Fig. 7-7

Fibers of

extracellular

matrix (ECM)

Glyco-

protein

Microfilaments

of cytoskeleton

Cholesterol

Peripheral

proteins

Integral

protein

CYTOPLASMIC SIDE

OF MEMBRANE

Glycolipid

EXTRACELLULAR

SIDE OF